A Tyrosyl-tRNA Synthetase Recognizes a Conserved tRNA-like Structural Motif in the Group I Intron Catalytic Core

The Neurospora crassa mitochondrial (mt) tyrosyl-tRNA synthetase (CYT-18 protein) functions in splicing group I introns, in addition to aminoacylating tRNA(Tyr). Here, we compared the CYT-18 binding sites in the N. crassa mt LSU and ND1 introns with that in N. crassa mt tRNA(Tyr) by constructing three-dimensional models based on chemical modification and RNA footprinting data. Remarkably, superimposition of the CYT-18 binding sites in the model structures revealed an extended three-dimensional overlap between the tRNA and the group I intron catalytic core. Our results provide insight into how an RNA-splicing factor can evolve from a cellular RNA-binding protein. Further, the structural similarities between group I introns and tRNAs are consistent with an evolutionary relationship and suggest a general mechanism for the evolution of complex catalytic RNAs.